The four building blocks

Object-oriented programming in C#

Explore encapsulation, abstraction, inheritance, and polymorphism through small C# examples, design checks, and a quick quiz.

Explore the concepts

Pick a concept. Read the code. Make the call.

Each example contrasts a common design problem with one possible improvement. The best design still depends on context.

Protect state; expose meaningful operations.

1Private state

2Validated method

3Safe object

What to notice

Public mutable fields let any caller break the account balance invariant.

C# / HTTP / SQL sample

A design to question

public class BankAccount
{
    public decimal Balance;
}

account.Balance = -5000;

Right or wrong: is this version a good fit?

Quick knowledge check

1 / 4

Which change best demonstrates encapsulation?

Based on our OOP interview guide. Examples are simplified for learning; adapt patterns to the requirements of your application.